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Project Report
ATC-259
A Description of the Interfaces between the
Weather Systems Processor (WSP) and the
Airport Surveillance Radar (ASR-9)
J.J. Saia
M.L. Stone
M.E. Weber
16 June 1997
Lincoln Laboratory
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
LEXINGTON, MASSACHUSETTS
Prepared for the Federal Aviation Administration,
Washington, D.C. 20591
This document is available to the public through
the National Technical Information Service,
Springfield, VA 22161
P
This document
is disseminated
Transportation
in the interest
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assumes tie liability
under the sponsorship
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of information
exchange.
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for its contents or use thereof.
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TECHNICAL
REPORT
STANDARD
TITLEPAGE
2. GovernmentAccessionNo.
1. Report No.
3. Recipient’sCatalogNo.
ATC-259
5. Report Date
4. Title and Subtitle
16June1997
A Description
of the Interfaces between the Weather Systems
Processor (WSP) and the Airport SurveiRance Radar (ASR-9)
6. PerformingOrganizationCode
8. PerformingOrganizationReportNo.
7. Author(s)
John J. Saia, Melvin
L. Stone, Mark
E. Weber
ATC-259
10. Work Unit No. (TRAIS)
9. PerformingOrganizationNameand Address
MIT Lincoln Laboratory
244 Wood Street
Lexington,
MA 02173-9108
11. Contractor GrantNo.
DTFAOl-93-Z-02012
13. Type of Repot-land PeriodCovered
2. SponsoringAgency Nameand Address
Department of Transportation
Federal Aviation Administration
Washington, DC 20591
Project
Report
14. SponsoringAgencyCode
15. SupplementaryNotes
This report
Technology,
is based on studies performed
at Lincoln Laboratory,
under Air Force Contract F19628-95-C-0002.
a center for research
operated
by Massachusetts
Institute
of
16. Abstract
The Weather Systems Processor (WSP) is an enhancement for the Federal Aviation Administration’s (FAA) current generation Airport
Surveillance Radars (ASR-9) that provides fully automated detection of microburst and gust front wind shear phenomena,estimates of storm cell
movement and extrapolated future position, and lo- and 20-minute predictions of the future position of gust fronts. The WSP also generates sixlevel weather reflectivity free of anomalous propagation induced ground clutter breakthrough. Alphanumeric and graphical displays provide
WSP-generated weather information to air traffic controllers and their supervisors.
This report describes the hardware, interfaces, timing and digital signal extraction from the ASR-9 necessary to support the WSP. The
digital interface circuitry between the WSP and the ASR-9, the control functions associated with the WSP, and strategies for performing system
test functions are described.
18. DistributionStatement
17. KeyWords
Airport
Surveillance
Radar
Wind Shear
Gust Front
19. Security Classif.(of this report)
Unclassified
FORM DOT F 1700.7 (8-72)
Radar data
Microburst
This document is available to the public through
National Technical Information
Service,
Springfield,
VA22161.
20. Security Classif.(of this page)
Unclassified
Reproduction
of completedpageauthorized
21. No. of Pages
58
the
22. Price
ABSTRACT
The Weather Systems Processor (WSP) is an enhancement for the Federal Aviation
Administration’s (FAA) current generation Airport Surveillance Radars (ASR-9) that provides
fully automated detection of microburst and gust front wind shearphenomena,estimatesof storm
cell movement and extrapolated future position, and lo- and 20-minute predictions of the future
position of gust fronts. The WSP also generatessix-level weather reflectivity free of anomalous
propagation induced ground clutter breakthrough. Alphanumeric and graphical displays provide
WSP-generatedweather information to air traffic controllers and their supervisors.
This report describes the hardware, interfaces, timing and digital signal extraction from the
ASR-9 necessaryto support the WSP. The digital interface circuitry between the WSP and the
ASR-9, the control functions associatedwith the WSP, and strategiesfor performing system test
functions are described.
...
111
TABLE OF CONTENTS
*
Section
Abstract
List of Illustrations
List of Tables
1.O INTRODUCTION
2.0 PERTINENT ASR-9 FEATURES
2.1 ASR-9 Overview
2.2 Antenna Feed Array
2.3 Radar Shelter Equipment
2.4 Six-Level Weather Processor
3.0 WEATHER SYSTEMS PROCESSOR OVERVIEW
3.1 Radar Data Acquisition
3.2 Radar Data Processor
3.3 Display Function
3.4 Remote Monitoring System
4.0 THE WSP RADAR DATA ACQUISITION FUNCTION
4.1 Microwave Signal Acquisition
4.1.1 Target Channel Waveguide Modifications
(Linear Polarization Mode)
4.1.2 Weather Channel Microwave Path Modifications
(Circular Polarization Mode)
4.1.3 WSP Receive Chain
4.2 Timing, Reference and Digital Signal Acquisition
4.2.1 Active Channel Stable Local
4.2.2 COHO
4.2.3 Azimuth Referencefor the WSP
4.2.4 Connection to the Target Channel A/D Converters
4.2.5 Basic Clock Generation
4.2.6 Rejection of Range Ambiguous Weather Echoes by Microstagger
4.2.7 Coherent ProcessingInterval
V
Pape
...
111
vii
vii
1
3
3
5
6
7
11
11
14
15
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18
21
22
24
26
27
27
28
28
29
29
TABLE OF CONTENTS
(Continued)
,
Section
4.3 Control Functions
4.3.1 On-Line Channel Selection
4.3.2 Target Channel Low Beam Selection
4.3.3 ASR-9 Weather Channel Beam Switch
4.3.4 WSP Receiver Input Control (SP3T)
4.3.5 Timing and Control of Alternate Beam Switching
4.3.6 Microwave “Preselector” Filter
4.3.7 RF Receive Chain Output
4.3.8 Sensitivity Time Control Attenuator
4.3.9 Six-Level Data Output Selection
4.3.10 “Off-line” or “Fault” Condition
4.4 Radar Data Processor(RDP) Input Synchronization
5.0 SUMMARY
ACRONYMS AND ABBREVIATIONS
REFERENCE
APPENDIX: SUPPLEMENTAL MATERIAL ON THE ASR-9 SIX-LEVEL
WEATHER CHANNEL
A. ASR-9 Six-Level Weather Receiver/ProcessorMonitoring
B. Master Timing
C. STCKalibration Generator (A4A 123)
D. Weather Test Target Generator(A4A124)
E. A/D Interrogate Pulse Generation (2.3.1.1.1.5)
F. Batch Control SequenceGeneration (2.3.1.1.1.6)
G. Batch Timing Signals Synchronization (2.3.1.1.1.7)
H. Receiver Calibration High/Low Beam Control
I. Receiver Control and Test Tone Generator
J. I&Q Development
vi
Page
32
32
33
33
33
33
34
34
34
34
34
35
37
39
41
43
43
43
44
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46
47
LIST OF ILLUSTRATIONS
Page
Figure
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
A-l.
Supervisor’s graphical situation display and local controller’s
ribbon display.
Antenna and high- and low-beam patterns.
ASR-9 feed array assembly (lOAl).
ASR-9 four-bay assembly, including the overheadarray of
microwave components for both channels.
ASR-9 Six Level Weather Channel waveguide components,shown
in their installed positions.
ASR-9 weather receiver/SCIP.
ASR-9 and WSP High Level Block Diagram.
Fourteen range azimuth windows exist.
Lincoln Laboratory prototype WSP Radar Data Processor
(RDP) configuration.
Simplified Waveguide Assembly Line Drawing.
Waveguide assembly. Original configuration and modified configuration.
Conceptual design diagram for WSP IAGC circuit.
Read and write order of digital samples showing both the CPIP
and ECIP array.
Timing diagram showing primary and secondaryinputs into
WSP radar data processor.
Lincoln Laboratory WSP Prototype RDA to RDP interface.
Bulk memory diagram showing the 960 weather target range cells,
the 13 CFAR cells used by the target channel, and the nominal
48 range cells used for calibration signals.
1
4
5
6
7
8
11
13
15
19
20
23
31
32
35
46
LIST OF TABLES
Pace
Table
ASR-9 to WSP Interconnections
1
Beam Switching Progressionfor WSP Controlled Microwave Switches
2
VDI-RPG MessageFormat
3
A-l ASR-9 Timing and Test Functions
vii
24
27
36
44
2.0 PERTINENT ASR-9 FEATURES
This section describes the architecture of the ASR-9 with emphasis on features pertinent to
integration of the WSP. The WSP functions, while often analogous to those of the ASR-9, will
be largely freestanding to facilitate integration, testing, and use with other coherent, highpowered radars with a suitable two-beam antennapattern and a dual-polarization feed.
2.1 ASR-9 Overview
The ASR-9, the latest generation Airport Surveillance Radar, was procured through a
contract by the FAA with Westinghouse Electric Corporation (now Northrop Grumman
Electronic Systems Division). Like earlier ASRs, its parameters are optimized for the detection
and tracking of aircraft throughout a terminal airspace volume extending from the surface to
24,000 feet above ground level (AGL) and out to as far’as 60 nmi. The transmitter operatesin the
2.7 to 2.9 GHz band with over one million watts of peak power, a 1.2 psec pulse, and better than
50 dB instability residue. The doubly-curved reflector antennaemploys two feed horns (figure 2)
which yield dual, overlapped elevation fan beams. The ASR-9 target channel and existing
weather channel process signals from the high beam at shorter ranges (nominally 15 nmi and
less) in order to reduce ground clutter illumination. Range-azimuth gated (RAG) microwave
switches then select the low beam input for longer range processing.
The antenna is scanned in azimuth with a nominal revolution period of 4.8 seconds. The
ASR-9 transmits a block-staggered pulse repetition frequency (PRF) waveform in order to
mitigate aircraft blind speeds. During the interval in which the antenna scans through one
azimuth beamwidth, ten pulses are transmitted at a “high-PRF”, followed by eight pulses at a
“low PRF”; the PRF ratio of these two pulse blocks is 7:9. Wind loading may causethe antenna
rotation rate to vary by up to 10 percent. “Fill” pulses at the low PRF may be inserted at the end
of the two pulse blocks (a so-called CPI-pair) in order to register the start of the next CPI-pair to
absolute azimuth.
The radar can transmit either linearly (vertical) or circularly (right hand) polarized
microwave energy. During clear conditions, the system will normally be in linear polarization
(LP) mode. During rainy conditions, the radar can be placed in circular polarization (CP) mode
in order to increase the signal to precipitation clutter ratio. This can be accomplished manually
through a switch setting on the ASR-9 control box, or automatically through a selection criterion
within the ASR-9 system. This criterion is based on the percentage coverage (over the entire
radar field of view) of precipitation echoesexceeding a “light rain” threshold.
A dedicated signal reception and processing channel measures and contours precipitation
reflectivity for display on controllers’ radar scopes (Data Entry and Display System or DEDS
and Bright Radar Indicator Tower Equipment or BRITE). This “weather channel” useshigh-pass
Doppler filters to suppress ground clutter, thresholds the precipitation echoes to six calibrated
intensity levels and performs spatial and scan-to-scan smoothing. During LP operation, the
weather channel input is from the target channel analog-digital (A/D) converters.When the radar
is in CP mode, separatemicrowave paths and a dedicated super-heterodynereceiver are used to
derive the appropriate (left hand circular) signal polarization from orthogonal ports on the
3
antenna feed horns. A “two-level” weather function embedded within the ASR-9’s target
processorprovides backup to this preferred six-level weather channel.
50
*50
ANTENNA GAIN
FREQUENCY = 2800 MHz
LOW BEAM
E-PORT
HIGH BEAM
E-PORT
LOW BEAM
H-PORT
HIGH BEAM
H-PORT
45
40
S/N 1081
34.1 dB
33.6 ciB
33.7 dB
32.8 dB
-45
f40
35
ANTENNA
PATTERN
30
i5; 25
25
i%
!I 20
BEACON
ANTENNA*
:
15
RADAR ANTENNA
10
5
0
-5
4038
36 34 32 30 28 26 24 22 20 18 16 14 12 10 8
6
4
2
0
RELATIVE POWER (dB)
Figure 2. Antenna and high- and low-beam patterns. The ASR-9 antenna is comprised of a reflector, two feed
horns, and a pedestal. The reflector carn’es an open array beacon antenna. The pattern shows the low beam at an
elevation angle of 03 This parameter is adjusted in accordance with the clutter environment at each site.
4
2.2 Antenna Feed Array
Figure 3 is a detail of the ASR-9 feed horn assembly. Shown are the high and low beam
feeds, associatedpolarizing sections and the input/output ports that are connected via waveguide
or coaxial paths to the transmitter and receiver sub-systemswithin the radar shelter. As noted,
circular polarization may be employed to reduce the magnitude of precipitation echoes in the
target channel. Precipitation echoesare delivered to the orthogonal or cross polarized port of the
orthomode transducer while target channel signals are delivered to the co-polarized signal port.
The polarizers in the high- and low-beam antennafeed horns employ electromechanically driven
phaseshifting units and 45” rectangular-to-squarewaveguide transitions.
FEED ARRAY ASSEMBLY
1OAl
(Right Side)
PHASING
SECTION
LO BEAM
FEED HORN ASSY
45 DEGREE
p2 LAUNCHER
POLARIZER
lOAlA
45 DEGREE (lOAlA2)
(lOAlSlJ2).
I
WAVEGUIDE /COAX w:lw
TRANSITION
-‘lJlp,
,~
‘HI BEAM
FEED HORN ASSY
Pl (1OAlCPlJl)
CPWl
Pl (1OAlCPWl)
-I
,
.
\
\
EAM SWITCH lOAlS1
T16310.30 (7 December 7990)
Fig. 1 l-22 ANTENNA (Unit 10)
MAJOR COMPONENTS
(Sheet 2 of 2)
276122-2
Figure 3. ASR-9 feed array assembly (IOAI).
5
2.3 Radar Shelter Equipment
Figure 4 depicts the ASR-9’s four-bay assembly consisting of redundant (“A” and “B”
channel) transmitter and receiver/processor cabinets, the Remote Monitoring System (RMS)
cabinet and the Six-Level Weather/Surveillance Communication Interface Processor(SCIP). The
four-bay assembly is housed in an environmentally controlled radar shelter building located next
to the antenna tower. This shelter is typically remote from the air traffic control tower and
unmanned. Technician visits to the shelter for fault diagnosis and repair are minimized through
use of the systemsRMS functions.
DC6
CHANNEL A I/
RCVRMICROWAVE
ASSY
:
DC2 -?
Ass
FROM: Ti6310.24 (1 December 1990)
FIGURE 1 l-26. ASR-9 SYSTEM PARTS
LOCATION DIAGRAM (Sheet 3 of 6)
2761226
Figure 4. ASR-3 four-bay assembly, including the overhead array of microwave components for both channels.
Figure 5 is a detail of the waveguide components of the ASR-9 Six Level Weather Channel
receiver. Physically, these are located in the radar shelter, above the four-bay assembly. As
describedin Section 4, these components are re-usedin the installation of the WSP.
6
ADAPTER
MICROWAVE
ASSY
SPDT SWITCH S5
BANDPASS
FILTER FL3
(Tuneable)
HY3’
WEATHEl
CHANNEI
HYI. HY2 = CIRCULATOR
HY3’= ISOLATOR
AT = ATTENUATOR/LOAD
AT9, AT10 = 50 52 (Termination)
CR = CRYSTAL DETECTOR
DC5, DC6, DC7 = BI-DIRECTIONAL COUPLER
-.
-
I
/
LOW NOISE AMP
(LNA) AR3
(RW
/
W/G-TOkOAX
TRANSITION
CP5
276122-l
Figure 5. ASR-9 Six Level Weather Channel waveguide components, shown in their installed positions.
2.4 Six-Level Weather Processor
The ASR-9 employs a common architecture, control, and data flow for all signal processing
functions in implementing its two target channels and six-level weather channel. Commencing
with the components on the antenna and carrying through the target or six-level weather data
output, the timing and signal processing, the grossblock diagrams of the two target channels,and
the six-level weather channel have a similar topology. All functions are implemented essentially
independently in each channel as shown in Figure 6. The synchronizer, monitoring and control,
RF-IF receiver components, A/D sampling (interrogate) pulses, batch timing, and calibration
functions employed by the six-level weather receiver is nearly identical in form to the
corresponding components in the ASR-9 target channels.In addition, the Weather Receiver/SCIP
function incorporates communications for target (surveillance) data, beacon (ATCBI) triggers,
and functional elements for formatting signals to feed a.local maintenancedisplay processor.
7
r-
~Tk~RE~I”EiiiSCi&~)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1
Figure 6. ASR-9 weather receiver/SCIP.
1
,
1
.T
1
The ASR-9 Weather channel has a RF-IF receiver that includes a low-noise front end, a
stable local oscillator, and mixer. A filtering and magnitude function is implemented in the sixlevel weather channel to handle the batches of A/D data comprised of samples from 18 pulses
generated during the transit of each beam width. A six-level weather detector thresholds the
processedbatch data and performs spatial and temporal smoothing. The resulting data are passed
to the messageinterface processor function of the system control for transmittal to modems and
the ASR-9 Remote SCIP. A local display processorfunction feeds six-level weather triggers and
video to a maintenance display.
9
3.0 WEATHER SYSTEMS PROCESSOR OVERVIEW
The WSP is comprised of four major functional elements: the Radar Data Acquisition @DA)
unit, the Radar Data Processor (RDP), the Display Function (DF) and a Remote Monitoring
System (RMS) (See Figure 7). The RDA acquires radio frequency (RF), timing and reference
signals from the ASR-9, as well as accomplishing various control functions describedbelow. The
RDP consists of commercial off-the-shelf (COTS) processors, housed in a VME chassis. The
RDP performs processing to suppressinterference such as ground clutter and out-of-trip weather,
to estimate precipitation reflectivity, Doppler velocity and spectrum width, and to generate
meteorological products. As shown, the RDP also hosts the drivers and media for data archiving.
The DF is comprised of the SDS and Ribbon Display. Terminals (RDTs) described previously;
these are moderately priced, COTS computer systems. The RMS monitors critical system
performance data to identify and isolate failures, and provides the operator interface to the WSP.
Received
Signals
Received
Signals
ASR-9
SYSTEM
High, Low, i%
L
Reference
Signals
’Receivers
Cha”ne’s) Reference
Signals
a ADC
Wind Shear
& RMS Data
Radar Data
Processor
DISPLAY
FUNCTIONS
T&ON
& ATCT
I
‘Spa;;$‘N,
DISPLAYS)
(W
I
#
Products
I
RF Control
6 Level Weather Less AP
-)
TO TRACON:
Radar Target Data,
6 Level Weather Less AP
AM-9
I
Clutter
Maps J
RMS < ==
Time Series
(Recorder) e
> WSP RMS
WSP
RMS
)
-
Local MDT
/
Figure 7. ASR-9 and WSP High Level Block Diagram.
3.1 Radar Data Acquisition
Broadly, the RDA accomplishesfour functions: (1) microwave signal acquisition; (2) timing,
referenceand digital signal acquisition; (3) control; and (4) RDP input synchronization.
Radio frequency (RF) signals from the linearly polarized (LP) and circularly polarized (CP)
high- and low-beam ports are connectedto a microwave switch matrix that makes the appropriate
beam selection, choosing between the high- and low-beam signal on alternate scans of the
antenna.Signals from the ASR-9 are monitored to determine which channel (A or B) and which
11
8
polarization are active. The RDA includes a dedicated, high dynamic range receive chain that
provides the primary input to the WSP’s Doppler processing algorithms. Intermediate frequency
(IF) test signals generatedby the ASR-9 circuits and coupled directly into the WSP are available
for use during the 4%range gate calibration interval which is programmed during the eight-pulse
coherent processing interval block. The weather test signal is used for off-line calibration. It is
controlled in range, azimuth, Doppler spectral width, and amplitude by the ASR-9 RMS.
Timing signals (e.g., COHO), antenna (azimuth) ‘and reference change pulses used by the
WSP are transmitted acrossthe interface. In addition, digitized quadrature samples are extracted
from the ASR-9’s existing A/D converters for use in extending storm reflectivity and motion
processing to the radar’s full coverage range, and in correcting for signal depolarization effects
as described later in this report.
The WSP control function determines the “start of scan,” and controls the RF switch matrix
as a function of radar polarization state (LP or CP), active channel selection, antenna scan count
and target channel Range-Azimuth Gating (RAG). (SeeFigure 8).
The primary output of the RDA is digitized quadrature samples from the dedicated WSP
receive chain, multiplexed with synchronous samples from the target channel A/D converters.
These are formatted in “pulse records,” each consisting of all (960) range gate quadrature
samples for each transmitted pulse repetition interval and accompanied by ancillary data
necessary for the RDP functions. The pulse records are clocked to the RDP via a 32-bit wide
parallel interface at a rate consistent with the ASR-9 range sampling interval of 1.3 MHz.
Details of these functions are describedin Section 4.
12
3.2 Radar Data Processor
The RDP is comprised of commercial off-the-shelf single-board computers, interconnected
through a VME-standard backplane. It accomplishes the entire suite of data processing
operations required to convert input radar quadrature samples to images of precipitation
reflectivity, Doppler velocity and spectrum width (“base data”),. and to extract user-oriented
meteorological products from these.
Figure 9 shows the RDP configuration currently deployed in the Lincoln Laboratory WSP
prototype. All processing cards are housed in a single, 19” VME-chassis. The RDP’s input is
from a single custom-built VME-data interface (VDI) card (part of the RDA) that formats
quadrature samples as described above and transfersthem onto a high-speed bus connecting a set
of signal processing cards. These accomplish ground clutter suppression, range/Doppler
ambiguity detection and generate a suite of base data images for input to the meteorological
detection algorithms. Each signal processing card handles a subsetof the range gates processed
by the WSP. Reference [l] describes the WSP base data generation algorithms and their
relationship to the control functions of the RDA.
Meteorological product generation is accomplished by single-board UNIX workstation
equivalent computers. Algorithms on these boards perform (1) microburst detection, (2) gust
front detection, tracking and future position extrapolation and (3) storm movement
estimation/future position extrapolation. A Global Positioning System (GPS) clock assignstime
to base data and meteorological products. Additional boards control data archiving (via small
computer systems interface (SCSI) disks and 8 mm tape drives) and a local meteorological data
display and monitoring console. The software within the RDP is single language (C/C++),
POSIX-compliant and includes a variety of unit-test, processmonitoring and debugging utilities.
14
Local Meteorological
Data Display
WSP
Host
. ----
wx Alg
Ret n
Signal
rrocessing
- .
FFlMMMM
PPEAAA
TowerKracon
G
P
s
R
8
0
4
x
O
6
C
P
u
SSMRRR
11
,
.
1
(To ASR-9)
c--w-Remote Situation/
RMS Displays
Figure 9. Lincoln Laboratory prototype WSP Radar Data Processor (RDP) configuration.
3.3 Display Function
Y
Meteorological products from the algorithms within the RDP are transmitted asynchronously
to the DF via a TCP-IP Ethernet protocol. There, they are decoded, used to generate runway
specific alphanumeric alerts where appropriate and displayed. The DFs accept numerous user
configuration commands (e.g., maximum range, active runway configurations, displayed product
selections, geographic reference map selections). Both “handshaking” and “broadcast” protocols
are available for communications between the RDP and each DF. The former is appropriate for
critical users such Air Traffic controllers who require extremely high reliability and immediate
fault detection. The broadcast protocol is more efficient for supporting remote users with less
critical responsibilities relative to the use of WSP products (for example, airline operations
personnel.)
15
Each DF unit consists of a Situation Display (a UNIX workstation or PC running a UNIX
environment) and one or more Ribbon Displays. The latter may be dedicated alphanumeric
monitors, or in some casesmay be implemented as separatevirtual windows on the SD. The DF
software is again C/C++ and employs many of the graphical interface tools and drivers used in
the RDP monitoring processes.
3.4 Remote Monitoring System
The WSP RMS function is comprised of:
1. Test points throughout the WSP system for collection of essential performance
monitoring and fault detection data (these may include built-in diagnostics within
the COTS components of the WSP);
2. An interface to the existing ASR-9 RMS to extract performance parameters
monitored by that system that are also critical to WSP (for example, transmitter
status);
3. Software for processing user commands, collecting and analyzing subsystem
performance monitoring data and fault indication, and for generating systems
alerts and alarms. The body of this software will run on a single-board computer
(68040 CPU) within the WSP VME-chassis;
4. A local Maintenance Data Terminal, the WSP technicians’ primary interface to
the WSP;
5. An interface to the FAA National Airspace System (NAS) Infrastructure
Monitoring System (NIMS), a central system monitoring facility under
development by FAA.
Details of the RMS performance monitoring and user interface functions are to be developed
by the WSP production contractor and approved by the FAA. Where appropriate, aspectsof the
WSP RMS-as they apply to RDA functions-are discussed in “concept” form in subsequent
sectionsof this report.
.
16
4.0 THE WSP RADAR DATA ACQUISITION
FUNCTION
The RDA provides the system-specific interface between an existing unit (the ASR-9) and
the often markedly different signal processing operations performed by the WSP. In combination
with the necessity of leaving existing ASR-9 search radar performance unaltered, the following
WSP processingrequirements dictate the design of the RDA.
1. Linearly or circularly polarized signals are processed from the high and low
beams on alternate scansusing the microwave components of the ASR-9 six-level
weather channel in combination with a new, high-dynamic range IF receiver. The
microwave circuits and IF receiver are configured to acquire and process the
weather signals from the two antennabeams on alternate antenna scans.
2. The WSP operatesalternately from either a high beam or a low beam connection.
The high-beam mode is a receive only (passive) mode which is utilized at short
range to reduce signals arising from ground clutter. The low beam is used for all
transmission, and for target detection it operates at pre-designated ranges beyond
local clutter. Control signals which select the required mode originate in STU A
(A4A120). In a particular beam mode, various windows are specified to define the
range and azimuth using variable site parameters(VSPs) (See Figure 8).
3.
A secondary input to the WSP Radar Data Processor is provided through the
active target channel receive chain and digitization circuits. These extend WSP
coverage to full range (LP mode) or allow for signal depolarization correction to
be implemented (CP mode).
4. To accommodate the large dynamic range of weather signals and clutter, an
instantaneous automatic gain control (IAGC) is used by the WSP IF receiver.
Signals used by the WSP for critical wind shear detection functions near the
airport (i.e., at short range) must be detected through this receiver as opposed to
the existing ASR-9 target channel receive chains.
5. A 27-pulse extended coherent processing interval (ECPI) is used by the WSP to
suppressground clutter and estimate base data fields.
6. The WSP signal processing function accounts for the presenceof fill pulses when
the ASR-9 antenna rotation slows and for signal loss due to depolarization of
circularly polarized waves.
7. A stand-alone synchronizer is used to ensure that A/D interrogation and other
WSP functions do not impact the operation of the target channel and to
accommodatespecial timing functions for the batch processing.
8. To account for fill pulses properly in forming a 27-pulse coherent processing
interval, a ring buffer is used to recover eight samples from the prior coherent
processing interval pair (CPIP). (When the antenna speed slows becauseof wind
loading, fill pulses occur until the appropriate antenna position is reached for the
17
next coherent processinginterval pair to begin. This operation registersthe ASR-9
geocontrol and censoring maps with the terrain). To facilitate identification of
data, each pulse repetition interval is marked with the bearing, time of day,
antenna beam position, and A/B channel selection and polarization. When
archived, date and time of day are recorded in the header.
9. Circular polarization signal intensity is corrected by appropriate combination of
the co- and cross-polarized signals. As the microwave signals transit rain, they
experience a phase shift that impacts the go-degree or quadrature relationship
established by the circular polarizer. This depolarizing effect reduces the signal
intensity output of the orthogonal (weather) port of the feed horn. To compensate
for the loss in signal intensity in the weather port, the signal from the co-polarized
(target channel) port is detected and combined with that of the orthogonal port to
obtain an accurateestimate of storm intensity.
4.1 Microwave Signal Acquisition
All of the WSP product generation algorithms utilize base data imagery constructed from
both high and low receive beam signals acquired nearly simultaneously (i.e., within a time
interval small relative to that required for significant change in the precipitation or wind field).
The two signal channels are either processedin parallel (for example to form “high” and “low”
beam reflectivity images) or in combination. For example, detection of microbursts requires
synthesis of a “dual-beam” velocity image that reflects the near surface component of the wind
field in thunderstorm outflows. Discrimination between gust front “thin line echoes” and
mimicking cloud features is aided by inter-comparison of reflectivity and Doppler velocity
imagery acquired from both beams. The reflectivity estimates which serve as the basis for
controllers’ six-level weather maps, and as the input to the storm motion algorithm, are
constructed as a range-dependent linear combination of power estimates derived from the two
beams.
4.1.1 Target Channel Waveguide Modifications (Linear Polarization Mode)
When operating in linearly polarized mode, both the high- and low-beam signals are derived
from the target channel (vertically or co- polarized) ports of the antenna. These ports in the
unmodified ASR-9 are connected by waveguide transmission circuits to the solid-state, highspeed, RAG high-low beam switch mounted above the equipment rack in the radar shelter.
Selector switches in each channel make connection from the waveguide, connected to the high
and low beam horns on the antenna,to the active (A or B) channel high-low beam switch.
4.1.1.1 Low Beam Interface
At short range, where Doppler processing and wind shear detection is operationally critical,
low beam signals must be processed through the dedicated, high-dynamic range WSP receive
chain. This is accomplished by shunting the unused low-beam signal to the WSP receiver over
the short range interval (nominally 0 to 15 nmi) where the target channel processeshigh beam
signals. At greater ranges, low beam signals for the WSP are acquired from the active target
channel A/D converter.
To accommodate the WSP with minimal impact on the performance of the low-beam signals
used by the target channel, the ASR-9 waveguide is rearranged(Seefigures 10 and 11). A second
18
high-speed, single-pole, double-throw (SPDT) waveguide switch is installed in each channel
(SWlOl, SW102) to extract the low-beam signal for processingin the RDA. The added switch is
slaved to the existing RAG beam switch (S2, S3) so as to direct the low-beam signal to the RDA
receiver when the high-beam horn is connected to the target channel receiver. The low-beam
signal is connected to the target channel receiver under ASR-9 RAG control beyond the nominal
15 nmi range.
The insertion loss associated with these added waveguide switches increases the ASR-9
target channel’s low-beam receiver minimum detectable signal (MDS) by approximately 0.5 dB.
This will decreasethe nominal detection range for a 1 square meter aircraft on the nose of the
beam by roughly 2 nmi. Since the ASR-9 system exceedsits detection envelope requirement by
more than this margin, the resulting decrease in performance is not expected to have an
operational impact on its aircraft surveillance function.
* 0mN” A
r-.----~-,
Cncular Polarization
High Beam
-
I
I
Waveguide
-0
1 Highl3wn
I
+
Low BeamJaveg$de
channelr
, 2
High & Low Beam
,?-,
Traffic
“B”
~
nSSw
Channel1
ASR-9
1
wsp
I
.
HF+SWg-
C-SW
Fl.3
I
>A
I
S6
I-,-,---------J
Figure 10. Simplified Waveguide Assembly Line Drawing.
19
1
ASR-9 WAVEGUIDES
LOW NOISE AMP
BANDPASS
UNI-DIRECTIONAL
RCVR PROTECTOR
NOTE:
1. CHANNEL
CHANNEL
CONTROL
B ILLUSTRATED:
A IS A MIRROR IMAGE OF B
2. WSP HARDWARE
INSERTION POINTS
FLEXGUIDE
(STC)
SPOT
W / G SWITCH
ORIGINAL CONFIGURATION
TO ASR9 OR WSP
RECEIVER
RF
INTERFACES
IFIEFI
/
SENSITIVITY
CAVITY-TUNED
* \ FILTER
r
LOW BEAM
ANTENNA INPUT
UIDE FROM T, R
RECEIVER ‘B
T/R
CIRCULATOR
POWER DIVIDER
TIME CONTROL
FLEXGUID
+
AVEGUIDE
SWITCH
WSP MODIFIED WAVEGUIDE CONFIGURATION
2761224
Figure 11. Waveguide assembly. Original conjiguration and modified conjfguration.
20
4.1.1.2 High Beam Interface
In contrast to the low beam mode of acquisition, the target channel’s use of high beam
signals at short range precludes their exclusive use by WSP. The target channel’s receive chain
design-specifically application of up to 60 dB Sensitivity Time Control (STC) attenuation, and
limited (63 dB) instantaneous dynamic range-preclude use of the target channel A/D converter
output for WSP. In linear polarization mode, the only feasible method for WSP acquisition of
high beam microwave signals is through insertion of a power divider in the target channel
receive path. Compensation for the insertion loss to the target channel is accomplished by
corresponding adjustment to the target channel STC attenuator, normally feasible over the short
range interval where high beam signals are employed by the target processor.
Three dl3 directional couplers (XPS 101, XPS102) are installed in the high-beam waveguides
feeding, respectively, the A and B target channel circuits. The second output of the on-line
channel high beam 3 & coupler is selectedby a SPDT XSW103 electromechanical switch and is
sent to an input of a single-pole, triple-throw (SP3T XSWlOS) switch whose output feeds the
receiving components used by the WSP.
As noted, the received signal energy loss to the target channel is compensatedfor by reducing
the STC attenuation applied downstream of the power divider. This is obviously feasible only
when the baseline STC exceeds 3 dB. Since the ASR-9’s nominal high-beam STC curve will
drop below 3 dB several miles before the nominal switch-over to low beam target channel
processing, the WSP’s power divider reduces upper elevation angle coverage over the last
several miles prior to this switch-over. In order to preclude a surveillance “hole” at high altitude,
the RAG high-low beam switch range may be moved in several miles. Analysis by engineers at
Northrop Grumman, the manufacturer of the ASR-9, have indicated that specified surveillance
coverage can be maintained with appropriate adjustments to the system’s Variable Site
Parameters(VSPs).
It is possible that clutter resulting from distant mountains necessitatesswitching back to the
high beam at ranges well beyond the nominal 15 nmi transition point. Since STC will normally
not be appropriate at such ranges, a potential loss of aircraft detection may occur in this region if
the target cross-sectionis less than 2 squaremeters.
Note that the minimum detectable signal for the high beam receive path is also reduced 3 dB
with this acquisition mode. This is unavoidable owing to the constraints associatedwith avoiding
significant impact to the ASR-9 target channel.
4.1.2 Weather Channel Microwave Path Modifications (Circular Polarization Mode)
As noted, weather processing functions during CP transmission mode must utilize signals
from the orthogonally polarized antennaports. The ASR-9 system has only one path through the
rotary joint for these signals and requires that high-low beam selection be accomplished at the
antenna. A high-speed switch (10AlSl) mounted on the antenna selects the high or low beam
and sends its output through a single coaxial run to the equipment shelter. The existing ASR-9
weather channel employs a RAG beam’selection mode (nominal high to low beam switch-over
occurs at 32 nmi) and processesonly one beam in any range gate.
When the WSP is on-line, its RDA assumescontrol of this beam switch to allow for nearsimultaneous (alternate scan) acquisition of signals from both beams in all range gates. The low
21
beam signal is processedby the WSP for all range gates for one full antenna scan; the switch
then toggles so that high beam signals are processed’during the following scan. As shown in
Figure 10, the WSP’s SP3T (XSW5) switch is connectedto the coaxial microwave path to select
the orthogonally polarized ports for input to the WSP RF/IF receive chain in CP mode.
It should be noted that the coaxial microwave paths employed by the ASR-9 for the
orthogonally polarized signals exhibit significantly greater transmission loss than the waveguide
runs used for the target channel inputs. Depending on the antennatower height and radar shelter
configuration, the loss through the coaxial runs may range from 3 to 7 dB. This will of course
result in an associatedincreasein minimum detectablesignal for the WSP.
In summary, the WSP interconnection to the ASR-9 microwave signals involves the
following elements shown in figure 10:
.
High-beam extraction via an added 3 dB power splitter (LP mode);
.
Low-beam extraction via an addedwaveguide SPDT switch (LP mode);
.
A or B channel selection; one for high beam, one for low beam (LP mode);
.
High- and low-beam CP extraction via reconnecting and reprogramming the
existing orthogonal port SPDT (1OAlS 1) switch to support alternating scan data
collection (CP mode); and
.
A single pole, triple throw (SP3T) switch to select the appropriate signal to the
WSP receive chain.
4.1.3 WSP Receive Chain
Microwave components of the WSP receive chain-largely re-used from the existing ASR-9
weather channel-are diagrammed in Figure 10. Switches S5 and S6 route input signals to the
appropriate pre-selector FL3 orPL4. These are band pass filters tuned to the “A” or “B” channel
transmitter frequencies; in combination with other ASR-9 components these filters eliminate
interference from out-of-band sources. In contrast to the ASR-9 target channel and existing
weather channel, the PIN-diode STC attenuator is under programmable map control, and is used
only in a limited number of range-azimuth sectors,to prevent low noise amplifier (LNA)
saturation.The LNA provides gain of approximately 24 dB; its dynamic range (nominally 95 dB)
setsthe limits within which the subsequentIF receiver and A/D converters operate. A stable local
oscillator (STALO) is mixed with the LNA output to derive the intermediate frequency output at
31.1 MHz. .
The microwave components of the receiver that are mounted above the radar cabinets are
shown in Figure 5.
4.1.3.1 Intermediate Frequency (IF) Receiver
The ASR-9 target channels and six-level weather processor use quadrature video (I&Q)
detectors and two 12-bit A/D converters. Servo circuits matches the amplitude and maintain the
phase quadrature of the I and Q signals. The digitized output comprised of two 12-bit words is
fed to the ASR-9 target channel or six-level weather processors.These well proven circuits could
22
be used by the WSP with the addition of instantaneousautomatic gain control (IAGC) at the IF
stage in order to match the A/D converter dynamic range interval to that of the front end LNA.
However, 14-bit or greater signal quantization is preferred, which will require additional circuit
modification. Northrop Grumman engineers are also examining a direct digitization coherent
detection receiver as describedbelow.
4.1.3.1.1 Direct Digitization
Recent developments in direct digitization of IF signals make possible the elimination of the
quadrature video circuits used in the ASR-9. To implement direct digitization, a reference
derived from the ASR-9 coherent local oscillator (COHO) is used to mix the WSP IF signal
down to 3.9 MHz with a 1.3 MHz bandwidth. This signal is sampled with an A/D converter
operating at 5.2 MHz. The I&Q data are recovered’ from the digital samples. The scheme,
referred to as “direct sampling quadrature detection,” eliminates one A/D converter and the
critical matching problems associated with quadrature video detectors. Note: The above
description is conceptual; the implemented concept may differ.
4.1.3.1.2 Instantaneous Automatic Gain Control (IAGC)
An instantaneousautomatic gain control (IAGC) is implemented on a pulse-to-pulse basis by
storing 960 range samples of the amplitude of WSP signals received during one pulse repetition
interval (PRI) and using them on a cell-by-cell basis to program the AGC attenuator and thereby
maintain the receiver within its linear range. This technique is possible, for the weather echoes
remain correlated for several pulse repetition intervals. A correction for the value of AGC
attenuation must be made on a cell-by-cell basis on the data for the subsequentset of samples.
The IAGC function requires new circuits to control its attenuator and an appropriate storage
register for the IAGC data must be added to store the 960 weather samples during a pulse
repetition interval (PRI). A ping-pong memory arrangement is needed for the IAGC operation
owing to the need to read the data from the previous sweepsfor processing the current sweep. A
conceptual block diagram is shown in Figure 12.
TO
Weather
Receiver
STC
Figure 12. Conceptual design diagram for WSP IAGC circuit. The circuit implemented may differ in topology.
23
4.2 Timing, Reference and Digital Signal Acquisition
In order to control its microwave signal acquisition circuits, drive its dedicated IF receive
chain and A/D converters, and perform its base data generation functions, the WSP requires nonintrusive accessto a number of ASR-9 internal system signals. The settings of the beam switches
used to select the appropriate ASR-9 antenna port output for the WSP receiver depend on the
radar’s active channel selection, polarization mode (LP or CP), RAG beam switch setting and a
scan counter derived from the Azimuth Reference Pulse/Azimuth Change Pulse sequence.The
WSP’s dedicated IF receiver requires the active channel coherent oscillator signal for derivation
of frequency sources necessaryfor down-conversion and A/D sample strobes. Signals defining
the time of pulse transmission synchronize the WSP quadrature samples to those generated
within the ASR-9 system. Finally, as noted ASR-9 target channel samples are necessary to
provide long range, low beam data (in LP mode), or to correct for signal depolarization biases(in
CP mode).
Table 1 defines the interfaces between the ASR-9 system and the WSP. For completeness,
the table lists the interfaces for necessarymicrowave signal acquisition (treated in Section 4.1)
and for feedback of WSP-generatedsix level weather into the ASR-9 system. Not all of the items
will be used by the WSP, for the functions may be derived by the WSP or may not be required.
Table 1
ASR-9 to WSP lntercdnnections
ASR9 Source
Functional
Name
Signal Name
WSP
Part Name /Tie Point
Part Name fI3e Point
Break-out “A” highbeam target channel,
for WSP
WSP “A” high beam
XPSlOl Cha. A
Power splitter
RF interface box: Cha.
“A” high beam
Break-out “8” highbeam target channel,
for WSP
WSP “B” high beam
XPS102 Cha. B
Power splitter
RF interface box: Cha.
“B” high beam
Break-out “A” lowbeam target channel
signals
WSP“A” low beam
XSWlOi Cha. A
Beam switch
RF interface box: Cha.
“A” low beam
Break-out “B” lowbeam target channel
signals
WSP “B” low beam
XSW102 Cha. B
Beam switch
RF interface box: Cha
“B” low beam
CP weather signals,
from antenna
CP Channel
CP high or low beam
on alternate scans
RF interface box:
CP high (or low) beam
{relocated DC7 into
RF interface box}
24
Table 1
(Continued)
WSP
ASR9 Source
Functional
Name
?F Test Target
3enerator(s)
Signal Name
RF test target
generator
Part Name /Tie Point
Part Name /Tie Point
Linear “‘A”, “B”, & CP
Used off-line as in
ASR-9
TBD
qF-IF TTG
selected COHO
COHOSP
A3S2-J4 (COHO
module)
WSP Receiver &
timing
,inear “A” - high or low
3eam selection
BEAMONLOI +/- &
BEAMONHI +/-
2A4A120: A61/A62 &
A63lA64
Matrix control
,inear “B” - high or low
team selection
BEAMONLOI +/- &
BEAMONH I +/-
5A4A120: A61/A62 &
A63lA64
Matrix control
Circular - high or low
beam selection
BEAMONLOI +/-
A5Jll:
RDA Controller
Pins 2 & 20
Polarization Selection - SBLPKPALinear or Circular
A4A121: C27
RDA Controller
Channel “A” or “8”
selection
WXCHA-/B
A4A121: C80
ASR-9
ASR-9 2/6 Level
automatic weather
selection
WXSEL2-/6
WXSEL2/6-
Card #217: A61
A62
TBD
Selected ACP
Synchronized
BNC A5Jl
To WSP processor
Selected ARP
Synchronized
BNC A5J2
To WSP processor
or
10.35 MHz clock
Test Signal
A4A114: Al 6/A17(+/-)
Timing and control
5.1 MHz clock
PLL5.1 MHZ
A4A114: C29
Timing and control
2.6 MHz clock
PLL2.6MHZ
A4AI 14: C26
Timing and control
Range clock (1.3 MHz)
SA1.3TSTGTS(+/-)
A4A120: A58lA59
Timing and control
RF Drive (Mod gate)
RGRFDRIVE-.
A4AI 22: A74
Reference
Pretrigger
PRETO
A4A120: C72
Timing and control
25
Table 1
(Continued)
WSP
ASR-9 Source
Functional
Name
Signal Nzime
Part Name nie Point
Part Name flie Point
Transmit Time Trigger
RGPRETO-
A4A122: A82
REF.:
2.3.1.1.3.3.2.2.2
Timing and control
Range zero
RGRO-
A4A120: B75
Timing and control
Interrogate
INTERROGATE
A4A121: 876
Ref. 2.3.1.1.3.3.2.3
Timing and control
CPI start
RGCPIST-
A4A120: B81
Reference
CPI end
RGCPIEND-
A4A120: C81
Reference
Calibration trigger
RGCALTRIG-
A4A103: A22
TBD
Channel “A” A to D output
ALTCI OO(+/-)
Adll35:
47148
25/26 thru
Weather Processor
RDA
Channel “B” A to D output
ALTC200(+/-)
A4J136: 25/26 thru
47148
Weather Processor
RDA
Interface for 6 level
weather less AP
CTSS(+/-)
Card #216: C12/C13
or
Card #I 10: C54/C55
TBD
Interface for 6 level
weather less AP
RTS3(+/-)
Card #216: Cl 4/C15
TBD
&rd #I 10: A78lA79
Interface for 6 level
weather less AP
RXD3(+/-)
Card #216: C16/C17
or
Card #I 10: C52C53
TBD
Interface for 6 level
weather less AP
TDX3(+/-)
Card #216: C18/C19
TBD
&rd #I 10: A81fA82
The following paragraphs provide details on to ASR-9 timing, reference and digital signal
interconnections.
4.2.1 Active Channel Stable Local
The ASR-9 STALO selectedby the on-line target channel is used and is connecteddirectly to
the mixer of the ASR-9 weather channel and will be used in place by the WSP.
26
4.2.2 COHO
The COHO is available on A352-J4 (COHOSP) at +2dBm level.
4.2.3 Azimuth Reference for the WSP
The ASR-9 derives its azimuth reference from one of the two pulse generators (with one online) located on the antenna pedestal. A train of 4096 azimuth change pulses are generated per
revolution of the antenna, and a reference pulse is generatedas the antennapassesnorth. In WSP
operation it is desirable to initiate azimuth scan data processing at different locations to prevent
missing data as the WSP switches between high and low beam during alternate scans of
operation. The switching transient takes several milliseconds and the associated loss of data
negates using one extended processing interval at the same azimuth location. The start-of-scan
for the WSP processing is advanced75 CPIP per revolution of the antenna,thus assuring that no
azimuth region will have a recurring loss of data. See Table 2. This results in the loss of one
Extended Coherent ProcessingInterval (ECPI) per scan.
Selection of which azimuth pulse generator is used for processing is determined by the
ASR-9.
Table 2
Beam Switching Progression
for WSP Controlled Microwave Switches
“scan”
0
Start Sector
(and Azimuth)
0 (0.0)
Stop Sector
74
1
75(105.5)
149
2
150 (210.9)
224
3
225 (316.4)
43
4
44(61.9)
118
253
31 (43.6)
.
.
105
254
106(149.1)
180
255
181 (254.5)
255
Sectors
Processed
O-255
o-74
75-255
o-149
150-255
O-224
225-255
O-255
o-43
44-255
Beam Switch
Position
Low
High
Low
High
Low
.
31-255
O-105
106-255
O-180
181-255
27
High
Low
High
4.2.3.1 Azimuth Change Pulse (ACP) Connection
The Azimuth Change Pulse appearsat the rear of the card cage on the STU trigger amplifier
(A4A221) pin 6. A more convenient location to acquire the signal is at the BNC connector on
A5Jl in the top of the four-bay cabinet. The signal is an 85.3 Hertz pulse and is 0 to +15 into
75 ohms. The driver schematic for this signal can be found in ASR-9 T16310.28, figure 1l-8,
page 8 of 17.
4.2.3.2 Azimuth Reference Pulse Generator
The Azimuth Reference Pulse (ARP) appears at the rear of a card cage on STU trigger
amplifier A4A221 pin 27. A more convenient location to acquire this signal is at the BNC
connector A5J2 in the top of the four-bay cabinet. The ARP which occurs as the antenna beam
passesthrough north is 0 to +15 volts into 75 ohms. The driver schematic can be found in ASR-9
Technical Instruction Manual TI6310.28, Figure 1l-8, Page 8 of 17.
The description for both signals can be found on Page 2-286 of Volume 4 of the ASR
Technical Instruction Manual T16310.28.
4.2.4 Connection to the Target Channel A/D Converters
Data for WSP operation are obtained from the target channel A/D converters for computation
of linear polarized six-level weather from the range of the RAG controlled high/low transition
(about 15 nmi) to the maximum 60 nmi range of the radar. In addition, the target channel A/D
converters from the co-polarized outputs from the antenna feeds provide data used when
operating with circular polarization to calculate the co-polarized component of weather intensity
over the same range interval. When operating with circular polarization, co-polarized intensity
values represent the depolarized signal component owing to differential phase shift resulting
from passing through rain and from reflection by non-spherical precipitation particles. Using the
sum of the squaresformula, the co-polarized signal intensity values will be combined with the
polarized signal intensity to obtain estimates of the total reflected power.
The A/D converter signals selected on an operating-channel basis are obtained from A4J135
(channel “A”) and A45136 (channel “B”) located in the ASR-9 weather channel bay four. Refer
to Technical Instruction Manual T16310.28,Figure 11-16, Page 1 of 9.
4.2.5 Basic Clock Generation
The ASR-9 generatesthree basic clock pulses at frequencies of 10.35,5.18, and 2.6 MHz. All
clocks are in phase with the 2.6 MHz reference from the on-line target channel,
receiver/processor (A or B). The ASR-9 weather and WSP channel basic clock generation
functions are synchronized to the on-line channel. All three clock frequencies are fed into the
staggered gate generation function which outputs the staggered gate pulses at frequencies of
0.65, 1.3,2.6, and 5.18 megahertz for use in the weather channel and elsewhere in the system as
clock data and synchronous enable signals. Signals as needed will be used by the WSP
(Reference:(2.3.1.1.1.1) T16310.36)
28
4.2.6 Rejection of Range Ambiguous Weather Echoes by Microstagger
An important feature of the WSP is its ability to reject second trip or range ambiguous
weather echoes by taking advantage of microstagger operation implemented by the ASR-9 to
eliminate range ambiguous aircraft echoes. It works effectively against rain clutter by
decorrelating secondtrip echoesby incrementing the pulse repetition interval two or three range
cells per pulse repetition interval‘
The timing and control circuits of the system automatically set up sampling of the weather
channel to correspond to the transmitted pulse offset. This function is referred to in the
TI manual (TI6310.28) as “variable timing” and is found in Section 2.3.1.1.3.3.2.2. Currently, all
operational ASR-9 systems are using variable timing. There is no action required for
integrating/operating the features with the WSP.
4.2.7 Coherent Processing Interval
The ASR-9 coherent processinginterval pair (CPIP) is the fundamental target data processing
interval based on the time required for the antenna to rotate 1.4 degrees. During this time, the
aforementioned group of ten high-PRF and eight low-PRF pulses is radiated and signals are
received. A CPIP occurs every 16 azimuth change pulses (ACP) yielding 256 CPIPs during one
rotation of the antenna.A comparable function will be derived directly by the WSP.
4.2.7.1 Trigger Puke Generation (TPG)
The 16th ACP gate trigger initiates the generation of the CPIP and time intervals within the
CPIP as well as the start of receiver events that occur within the CPIP. The trigger pulse timing is
determined by a site-dependentpair of pulse repetition frequencies which are VSPs assignedby
the frequency manager and implemented at the time of installation. For a particular PRF set, the
trigger generator automatically varies the pulse repetition interval (microstagger) to eliminate
range-ambiguous targets. The variable-rate timing is implemented using numbers which are
stored on the RAG, generator memory board. The ACP gate trigger synchronizes the trigger
output pulses to the real-time azimuth position of the antenna.A real-time binary count of range
cells which occurs within each pulse repetition time (PRT) is also provided by the trigger pulse
generation function. There are 18 or more PRTs in a CPIP, depending on the rotation rate of the
antenna. Should the antenna speedslow down due to wind loading, up to three fill pulses at the
high-pulse repetition frequency of the CPIP are used to fill the gap. Should the antenna speedup
significantly, a “short” PRT is usedto create 18 pulses in the CPIP without fill pulses.
Within each PRT, the ASR-9 processesdate in l/16 nmi increments, referred to as “range
cells” (a total of 973 cells corresponding to 60:
nautical miles are used). The last 13 cells are
carried to provide data for the constant false-alarm rate function in the target processor.
The WSP employs 27 pulses in its coherent processing interval (Figure 13) and therefore
uses a ring-buffer to acquire and store the quantized receiver data. It recovers eight pulses from
the previous block, independent of the presence of fill pulses. The data are stored on a rangeordered basis for the 27 PIUS and read into the signal processorin batch order, i.e., 27 PRIs, one
range at a time.
29
4.2.7.1.1 AID Data Manipulation
The read-write algorithm used by the two-block, 18-pulse data structure of the ASR-9 target
channel processor is transformed into a three-block, 27-pulse data analogue for the WSP. The
write order distributes I and Q data for 973 range cells each pulse repetition interval. The WSP
stores range-ordered data continuously. The high and low CPIs operate with two different pulse
repetition frequencies to eliminate Doppler blind speed effects in the target detection. This
arrangement, which accomodates the need of the target channel and the requirement of
processing27 PRIs for the WSP extended coherent processing interval, establishesa batch order
as shown in Figure 13.
..
30
BUI
bRTsOR
.-#
INTERPULSE
PERIODS
RANGE
ORDER
(WRITE)
Extended
Coherent Processing
interval (ECPI)
17,514 RANGE
CELLS
R
ONE BAT
II
Cel
BULK MEtl
~~RPZZ%G~GT~
BATCH ORDER (READ)
Modified TI 6310.28, Figure Z-33, Page Z-147
Figure 13. Read and write order of digital samples showing both the CPIP and ECIP array.
31
4.3 Control Functions
As described previously, the WSP RDA controls a network of microwave switches which
route appropriate signals to the WSP receive chain. When on-line, the WSP must determine the
appropriate positions for these switches using high speed logic devices, and generate suitable
drive signals. The sequencing of signals processedby the WSP RDP is summarized in Figure 14.
Special timing signals are provided for implementing the required switching of the microwave
circuits and digital signals. The ASR-9 functions are described in ASR-9 Technical Instruction
Manual TI6310.28 and will coveredhere only as they relate to their role in the WSP.
-
-yD#lI
I---)i=
“FEr
I
’
15 nm
I
Range
nm
I
Linear
Low Beam
1
-------
I
ASR-9 Active
A to D Converter
ASR-9 12 Bits Radar Data
(Linear Low Beam Only)
I
Linear
High Beam
I
45nm
a-w-
14 Bits WSP
Radar Data
I
60nm
---a---
-------
14 Bits WSP
Radar Dats
Circular
Low Beam
14 Bits WSP
Radar Data
I
14 Bits WSP
Radar Data
Circular
High Beam
ASR-9 Active
A to D Converter
Co-Polarized
ODD
I
I
--B--m-
Scan #3
___ct_
I
High Beam
I
Low Beam
High Beam Low Beam
12 Bits Traffic Channel Radar Data
Figure 14. Timing diagram showing primary and secondary inputs into WSP radar data processor.
The RDA must also control an STC unit dedicated to the WSP input paths. The WSP must
recognize when it has entered either a “fault” or “off-line” state, and return control of those
switches embedded within the ASR-9 to that system.
4.3.1 On-Line Channel Selection
Beam switches XSW103 and XSW104 (see Figure 10) are under WSP control to provide
WSP accessto the active channel (“A” or “B”), co-polarized (target channel) microwave signals.
32
4.32 Target Channel Low Beam Selection
Beam switches XSWlOl (“A” channel) and XSW102 (“B” channel) are controlled to provide
WSP access to the active channel, co-polarized, low beam microwave signals. The control
signals are slaved to the active channel RAG beam select signal so as to divert low beam data to
the WSP only when it is not in use by the target channel. The waveguide is connected to the
ASR-9 in the default condition.
4.3.3 ASR-9 Weather Channel Beam Switch
Control of the ASR-9 weather channel’s coaxial beam switch (10AlSl) is assumedby the
WSP when on-line in the CP mode. As opposed to the fast, RAG switching commanded by the
ASR-9 weather channel, the WSP toggles this switch between high and low beams on an
“alternating” scan basis as describedbelow.
4.3.4 WSP Receiver Input Control (SP3T)
The single-pole, triple throw switch XSW105 is controlled by the RDA to select the
appropriate microwave input to the WSP receive chain. During CP transmission, this switch is
latched to the output of the cross-polarized channel coaxial switch (10AlSl). During LP
transmission, the switch toggles-on an alternating scan basis-between the high and low beam
inputs from the target channel microwave paths.
4.3.5 Timing and Control of Alternate Beam Switching
The operation of the WSP with alternating scanbeam switching and a single receiver channel
requires dedicated timing circuitry in which the antenna change pulses (ACPs) and antenna
reference pulses (ARPs), suitably processed,play a key role in controlling the above microwave
switch functions.
4.3.5.1 Scan Initiation Stepping
The WSP timing unit will receive input signals from the antenna reference pulse (ARP) and
antenna change pulse (ACP) circuits of the ASR-9. The transition between high and low beam
takes place within a 1.4 degree interval (l/256 of a circle), defined, in the ASR-9, as a coherent
processing interval pair (CPIP, approximately 20 milliseconds). Owing to the use of
electromechanically driven microwave switches that transition in a few milliseconds, one
extended coherent processing interval will be lost during each scan. To minimize repeatedly
missing critical data at the same location, the position of the alternating scan transition will be
stepped in azimuth after each scan. The stepping interval is equal to 75 antenna azimuth
beamwidths, or 105.5 degrees.The beam switching~progressionis described in Table 2.
The timing for the switching transitions for selection of the high and low beam will be
synchronized to the corresponding beam position and radar transmission to assure that
registration of the precipitation and clutter maps are preserved.It is not necessaryto initialize the
start of the above sequence at the Antenna Reference Position; any CPIP start pulse is
appropriate to begin counting the 75 CPIP interval used to rotate the high-low beam transition.
33
4.3.6 Microwave ‘Preselector” Filter
Switches S5 and S6 are controlled by the WSP when on-line to select the microwave
bandpassfilter (FL3 or PL4) matched to the active channel transmitter frequency.
4.3.7 RF Receive Chain Output
As shown in figure 10, the RF receiving chain components of the ASR-9’s six level weather
channel are sharedby the WSP. When on-line, the WSP RDA sets switch XSW107 to direct this
output to the WSP’s high dynamic range II? receiver.
4.3.8 Sensitivity Time Control Attenuator
The STC unit within the shared WSP/Six-Level Weather Channel RF train is controlled by
the RDA when the WSP is on-line. As noted, the WSP normally employs significantly less
attenuation than is used by the existing weather channel owing to the increaseddynamic range of
its IP receive chain and digitization circuits. The RDA controls the STC unit on a range-azimuth
dependent basis using site-adaptable maps. Eight STC maps are employed to cover all
combinations of polarization (CP or LP), active channel (A or B) and beam selection (high or
low).
4.3.9 Six-Level Data Output Selection
The six-level weather feed to the local maintenance PPI display, and to controller’s DEDS
and BRITE display is switched to the on-line processor, i.e., either the WSP or the ASR-9 sixlevel output ports. The switch function is installed by cutting four wires on the backplane and
installing appropriate SPDT logic to route either the WSP output, suitably formatted and
controlled, or the original ASR-9 six-level weather data to the transmission circuits of the
ASR-9. Refer to T16310.36 card #216 and card #llO, appendix X 645A196-1 rev. AG sheet
#126 [RXD3T(+/-) and RTS (+/-)I. [Note: This reference is optional as there may be less
invasive use of the backplane wiring. The above mentioned circuit revisions communicate only
six-level weather information from the.WSP or the ASR-9 weather channel to the controller’s
ARTS display processor via circuits MIP and SCIP already in place in the ASR-9. Separate
circuits that combine the product generator outputs are used to feed the dedicated WSP display
functions in the TRACON and the ATCT.]
4.3.10 “Off-line” or ‘Fault” Condition
If the WSP is placed off-line due to detection of a fault condition by its RMS, or through user
manual action, microwave switches must be latched in appropriate positions and ASR-9 system
control functions restored so that baseline ASR-9 system functions and operation are unaffected.
These default switch positions shall correspond to the unenergized state. The following actions
are required:
1. Switches XSW 101 and XSW 102 are latched so as to “hardwire” the same sense
polarization low beam antenna outputs to the input of the target channel RAG
beam switches (S2 and S3).
34
2. Control of the weather channel preselector switches (S5 and S6) and STC unit is
returned to the ASR-9 six-level weather channel.
3. Switch XSW107 is latched so at to provide RF receive chain output to the existing
ASR-9 six-level weather channel IF receiver, digitization and processing circuits.
4. Control of the cross-polarized signal coaxial waveguide switch (10AlSl) is
returned to the ASR-9. This allows for resumption of the RAG beam selection
mode required by the ASR-9. six-level weather channel.
5. The SP3T switch XSW105 is latched so as to hardwire the output of the crosspolarized coaxial waveguide switch (1OAlS 1) to the weather channel receiver.
6. Control of the six-level weather reflectivity .feed to local maintenance, DEDS and
BRITE displays is returned to the ASR-9 system.
4.4 Radar Data Processor (RDP) Input Synchronization
The output of the RDA to the RDP are uniformly formatted “pulse records,” clocked over a
parallel bus at a rate consistent with the range-gate sampling interval of the ASR-9 system.
Figure 15 is a high-level block diagram of the digital interface used in the Lincoln Laboratory
WSP prototype to interconnect the RDA and RDP functions. For each ASR-9 pulse-repetition
interval (PRI), the VME digital interface (VDI) transmits a fixed length (32 bit) messageonto a
high-speed bus within the RDP. To create this message,the VDI performs minor reformatting of
the fixed length messagetransmitted by the radar digital interface (RDI). The RDI-VDI message
interface allows only 3 1 information bits per word because the most significant bit (bit 31) is
used to identify the first word of a frame. The VDI messagesare clocked into the RDP at a rate
of 2.6M words per second.
Custom
1 frame/p&
1930 words/frame,
31 information bits/word
b-,
ASR-9,
RF Switches, M
WSP Receiver
Radar
Digital
Interface
WI)
Framing
Bit
b
Clock
2.6 MHZ
Acquisition,
Counting,
Switch Control
l
R/N-T
1 frame/prt,
1930 words/frame,
32 information bits/word
VME Side
Digital
interface
WI)
4
),
Svnc\
RPG
Strobe
Reformatting
Figure 15. Lincoln Laboi-atory WSP Prototype RDA to RDP interface.
Table 3 identifies the data elements included in the message frames transmitted from the
RDA to the RDP. To distinguish whether data are acquired from the ASR-9 system, or created
within the WSP RDA, the source for each messageelement is indicated in the third column of
the table.
35
Table 3
VDI-RPG Message Format
WORD
I
Bits
Bits
Bits
Bits
3-O:
7-4:
15-8:
18-l 6:
Bit 19:
Bit 20:
Bit 21:
Bit 22:
Bit 23:
Bit 24:
1, 2
Bits 30-25:
Bit 31:
Bit 30-O:
4
Bit 31:
Bits 11-O:
Bits 31-l 2:
Bits 11-O:
5
Bits 31-12:
Bits 30-O:
3
6
7
8
9
IDENTlilER
Year Ones
Year Tens
Drive ID (0x01)
XSW105 Status:
001 - LP, low beam;
010 - LP, high beam;
loo-CP
XSW103 & 104 Status
A=O, B=l
Channel: A=O, B=l
Polarization: L=l , CP=O
Scan: even=O, odd=1
XSW107 Switch Position:
O=ASR-9,i =WSP
STC Switch Position:
O=ASR-9,l =WSP
unused
0
Fast Time Count
(f = 1.3 Mhz)
0
Bit 31:
Bits 31-O:
Azimuth
0
Scan Count (increments
every ARP)
0
Frame Count (increments
every PRT)
0
Test Pattern Ox2AAA5555
Bits 31-O:
Bits 31-O:
Bits 31-O:
Test Pattern Ox5555AAAA
Test Pattern Ox2AAA5555
Test Pattern Ox5555AAAA
FOR 960 RANGE CELLS
Bits 1-O:
10+2n
Bits 13-2:
Bits 15-14:
Bits 27-l 6:
Bits 28:
Bits 31-29:
Bits 13-O:
11+2n
Bits 27-14:
Bits 31-28:
SOURCE
RDI
RDI
RDI
WSP RF Switch
WSP RF Switch
ASR9 Backplane
ASR-9 Backplane
RDI
RDI
RDI
RDI
RDI
RDI
RDI
RDI
RDI
RDI
RDI
RDI
(range sample n = 0 through 959):
0*
ASR9 backplane
Target Channel Linear I
o*
ASR-9 backplane
Target Channel Linear Q
ASR-9
backplane
High or Low Beam (High=!)
0*
WSP Receiver I
RDI A/D Converter
WSP Receiver Q
RDI A/D Converter
AGC(3:O)
WSP Receiver IAGC
* For each range cell, a total of 62 information bits are available in the Phase II prototype
RDI-VDI interface. Of these, 25 bits are dedicated to the target channel I & Q bits and the
High/Low beam indication bit. Therefore, 37 bits are available in each range cell to transfer
the WSP receiver I & Q bits, AGC bits, and a saturation indicator.
36
5.0 SUMMARY
As discussedin this report, the required inputs to the WSP can be acquired from the ASR-9
through implementation of suitable microwave and digital signal interfaces, appropriately
controlled by logic devices within the WSP. Although detailed design of this interface will be
accomplished by the WSP implementation contractor, we expect that many features described
herein will be preserved at least functionally.
Many, but not all, of the interface components described herein have been implemented and
validated using the Lincoln Laboratory ASR-WSP testbed in Albuquerque, NM and Lexington,
MA. Items that have not yet been installed on theseWSP exploratory units include:
1. The recommended downconversion IF filter with instantaneousAutomatic Gain
Control calculated using data from the preceding PRI;
2. The interface hardware and software needed to feed WSP-generated six-level
weather back into the ASR-9 system for output onto existing controllers’ radar
scopes;
3. Use of the RF test signals from the ASR-9,
4. Built-in failure sensing of the WSP,
5. BIT/FIT,and
6. RMS functions.
Implementation and evaluation of an appropriate IF receiver (item 1) and six-level weather
feedback interface (item 2) are underway via a contract from Lincoln Laboratory to Northrop
Grumman Corporation. In addition, some elements of WSP BIT/FIT and RMS functions are
being developed for evaluation under this contract. These subsystemswill be implemented on the
WSP exploratory units and evaluated during the 1997 convective storm season.The remaining
items listed above will be accomplished during WSP full-scale development.
37
ACRONYMS AND ABBREVIATIONS
ACP
AGC
AGL
AP
ASR-9
ATCBI
ATCT
BIT
BIT/FIT
BNC
BRITE
CFAR
CMT
COHO
COTS
CP
CPI
CPIENO
CPIP
DEDS
DF
DRI
ECPI
EEPROM
FAA
GPS
I&Q
IAGC
IF
LED
LNA
LP
MDS
MTD
NAS
NIMS
PLL
PPI
PRETO
PRF
PRI
PRT
RAG
Analog to Digital
Antenna Change Pulse
Automatic Gain Control
Above Ground Level
Anomalous Propagation
Azimuth ReferencePulse
Airport Surveillance Radar
Air Traffic Control Beacon Target Interrogator
Air Traffic Control Tower
Built-in Test
Built-in Test/Fault-Isolation Test
Bayonet Neil1 and Councelman connector
Bright Radar Indicator Tower Equipment
Constant False-Alarm Rate
Configuration, Monitor, and Test data bus
Coherent Local Oscillator
Commercial Off-The-Shelf
Circularly Polarized, Circular Polarization
Coherent ProcessingInterval
End of CPI
Coherent ProcessingInterval Pair
Data Entry and Display System
Display Function
Data Recorder Interface
Extended Coherent ProcessingInterval
Electrically Erasable Programmable Read-Only Memory
Federal Aviation Administration’
Global Positioning System
In phaseand Quadrature
InstantaneousAutomatic Gain Control
Intermediate Frequency
Light Emitting Diode
Low Noise Amplifier
Linearly Polarized, Linear Polarization
Minimum Detectable Signal
MessageInterface Processor
Moving Target Detector
National Airspace System
National Airspace System Infrastructure Monitoring System
PhaseLocked Loop
Plan Position Indicator
Pretrigger 0
Pulse Repetition Frequency
Pulse Repetition Interval
Pulse Repetition Time
Range Azimuth Gate
39
RDA
RDI
RDP
RDT
RI?
RF-IF
RGPRETO
RMS
RPG
SCIP
SCSI
SD
SP3T
SPDT
STALO
STC
STU
TDWR
TPG
TRACON
TTG
VDI
VME
VSP
WSP
Radar Data Acquisition
Radar Digital Interface
Radar Data Processor
Ribbon Display Terminal (an alphanumeric display)
Radio Frequency
Radio Frequency-Intermediate Frequency
Range Pretrigger
Remote Monitoring System
Radar Product Generator
Surveillance Communications Interface Processor
Small Computer Systems Interface
Situation Display
Single-Pole, Triple-Throw
Single-Pole, Double-Throw
Stable Local Oscillator
Sensitivity Time Control
System Timing Unit
Terminal Doppler Weather Radar
Trigger Pulse Generation
Terminal Radar Control Facility
Test Target Generator
VME-Data Interface
An IEEE standardchassisbackplane
Variable Site Parameters
Weather SystemsProcessor
40
REFERENCE
i31
Mark E. Weber, “ASR Weather Systems Processor (WSP) Signal Processing
Algorithms,” Lexington, MA, MIT Lincoln Laboratory, Project Report ATC-255,
publication pending.
41
APPENDIX
SUPPLEMENTAL MATERIAL
ON THE ASR-9 SIX-LEVEL WEATHER CHANNEL
The following paragraphsprovide supplemental information on six-level weather processor
functions. Where provided, the parenthetical numbers in the sub-section headings refer to the
ASR-9 Technical Instruction Manual paragraphwhere the associatedfunction is described.
c
A. ASR-9 Six-Level Weather Receiver/Processor Monitoring
In the original ASR-9 configuration, the six-level weather data are generated in a subsystem
which includes the weather channel low-noise amplifier, a superheterodyne receiver, digital
converters,a digital processor,and processesdiagnostics and VSPs from the Remote Monitoring
Subsystem (RMS) and azimuth data (ACP and ARP) from the antenna. The monitoring and
control functions associated with the ASR-9 distribute VSPs to the timing unit (synchronizer,
filtering and magnitude function, and to the six-level detection functions). In addition to the
monitoring and control functions, a set of BIT/FIT functions are implemented in the ASR-9 sixlevel weather processor. The weather receiver cabinet (Number 4) also contains switches and
light emitting diodes (LEDs) which are used by maintenance personnel at the site. A local
display processorfunction is implemented to feed a maintenance display unit also located at the
local radar site. Figure 6, the weather receiver/SCIP overview block diagram, contains the major
functional elements and signal flows to and from the weather channel.
The following functions are performed by the ASR-9: a) calibration batch data processing,
b) weather data processing, and c) BIT batch data processing. The BIT functions are all
performed during the dead time preceding the next PRI. The synchronizer function initializes a
routine that checks the RF-IF receiver, the filtering and magnitude function, and the monitoring
and control function. The batch data processing is a test mode initialized by the remote
monitoring system and is transparentto operation of the RF-IF receiver.
B. Master Timing
The synchronizer is the primary source of timing signals for the entire ASR-9. In addition to
providing all the master clock signals used both by the target and weather channels, it
implements the following:
The system timing unit (Table A-l) develops various clocks, selects the antenna high/low
beam horn, and performs BIT for the synchronizer. The BIT function tests the trigger signals
from the RF test target generator A4A125, the range azimuth generator (A4A122), the
STCYcalibration generator (A4A123), and the batch control sequencer A4A117. The BIT test
information is routed to the monitoring and control function. There the configuration, monitor,
and test data bus (CMT), the range azimuth gate generator (A4A122), and the triggers generated
by the RAG are used in conjunction with the system timing unit A (A4A120) and the RF test
generator (A4A124) in the RAG generation to determine system status. In addition, some of the
triggers are also used in the filtering and magnitude process and in the target signal processor,
weather receiver/SCIP, and the two-level weather detector. The triggers are tested by the BIT
circuitry located in the STU A (A4A120). The RAG generator also contains the function that
43
synchronizes the antenna position pulses with range sample pulses. The function of the STU B
(A4A121) is to provide an interface between the transmitter, RF/if receiver, frequency generator,
weather receiver/SCIP, and the monitoring control function. The STU B receives radar mode
data from the weather receiver/SCIP and usesthis data to generatecontrol signals that are output
to the transmitter. It also receives buffered triggers from the RAG generator and outputs them to
the transmitter. One of these is a pre-trigger which generatesprogram delay triggers used for
system alignment. The STU B also outputs system control signals to the RF-IF receiver and data
processing controls to the two-level weather detector. Some of the signals generated on STU B
are testedon BIT located in STU A.
Table A-l ’
ASR-9 Timing and Test Functions
Abbreviated
Name Designation
Name
I
1
Reference *
Batch Control Sequencer
BCS
A4All7
PLL channel Sync. PLL channel Sync.
PLL
A4A114
System Timing Unit A
STUA
A4Al20
System Timing Unit B
STUB
A4Ai 21
RAG
A4Al22
STCXAL
A4A123
l-l-G
A4Al24
RAG
STCkalibration generator
.
RF Test Target Generator
* Refers to ASR-9 circuit card designation
C. STCKalibration
Generator (A4Al23)
The STCKalibration Generator provides signals that control receiver gain during the live
time and generates calibration control signals during the calibrate time. Both RF and IF+
calibration signals are generated during the calibrate time. The IF signals are generated by the
RF-IF receiver while the RF test signals are generatedby the RF test target generator (A4A124).
A control signal is also produced which controls the sampling of the test target data for the
filtering and magnitude processor. The STCKalibration Generator is controlled by the
monitoring and control function via the CMT bus. This unit’s outputs are tested by BIT located
on STU A.
D. Weather Test Target Generator (li4A124)
The weather test target generator provides two- and six-level weather digital signals. Target
signals are used for testing the target receiver/processor in the A and B channels. The weather
digital test target signals are synchronized with the RF.test target data by the target A and target
B signals from the target receiver/processors.The board also receives channel control signals
(CHA-/B) from the local system control processor to produce RF and IF control signals. These
signals are output to target receiver/processor A and B, the RF filters, and the RF-IF receiver.
BIT testing of the test target generator board signals is performed on the STU A board. The test
target generator is controlled by the monitoring and control function board via the CMT data bus.
44
E. A/D Interrogate Pulse Generation (2.3.1.1.1.5)
The A/D pulse function is used on the ASR-9 A/D converter board of the RF-IF receiver for
A/D interrogations. The PRT start triggers PRETO. RGPRETO enables the output of the
interrogate signal INTERROGATE. A similar function is required for the WSP.
Becauseof the need to have a fine adjustment of the INTERROGATE while maintaining its
phase synchronization with the radar timing, a 10.35 MHz clock shifts the 1.3 MHz pulses
through a delay register to maintain phasefor every PRT.
.
F. Batch Control Sequence Generation (2.3.1.1.1.6)
The batch control generates a series of signals that sequentially order the flow of weather
data, commencing at the filter and magnitude processor and proceeding all through six-level
weather detector/processorfunctions. A batch of data includes the weather, test, and calibration
data processedduring one CPIP. The batch control signals are structured by a pre-programmed
memory in the batch control sequence.The process is started by the CPIP start trigger from a
trigger pulse generator. BIT/FIT logic signals are scheduled by this process (See Figure A-l).
Figure A-l illustrates the memory requirements associatedwith a CPIP.
G. Batch Timing Signals Synchronization (2.3.1.1.1.7)
The batch time signals synchronization function develops the antenna polarization flag
(circular or linear) and the north indicator (antenna at zero degrees, and the level of weather
flag). The ASR-9 six-level weather detector uses batch time signals to select pre-programmed
VSPs that define weather detection threshold values in the ASR-9 Wx channel. The batch time
CPIP clock which is enabled by the CPIP start trigger from the trigger pulse generator function
synchronizesthe batch time signals to the batch processing.
45
2042
.
LIVE
DATA
LIVE
DATA
LIVE
DATA
973
RC%:
IandQ
v)
=
8
Q)
F
8
2*48
CALIBRATION
DATA
CALIBRATION
DATA
UNUSED
0 A
48
AL
+8PRTe+++
lOPRTe+9PRTe+j
MODIFIED FOR WSP
Bulk Memory Data Diagram
TI 8810.28 (01 Dec. 90) pg 2-151
WSP bulk memory located in the Radar Data Acquisition
unit.
Figure A-l. Bulk memory diagram showing the 960 weather target range cells, the 13 CFAR cells used by the
target channel, and the nominal 48 range cells usedfor calibration signals.
H. Receiver Calibration High/Low Beam Control
During normal operation of the radar, calibration of the receiver and the A/D converter are
constantly being performed by the monitoring and control function. Details are found in
TI manual TI6310.28.
I. Receiver Control and Test Tone Generator’
In the ASR-9 weather channel, the RF-to-IF conversion is coupled through an isolator and
amplifier to provide input matching. The overall noise figure of the front end is 6 dB. The
amplified RF is applied to a go-degree hybrid, a part of an image generation and image rejection
’ The circuit will be modified with the direct digital conversion circuit.
46
scheme. The image signal is effectively canceled by the hybrid arrangement and subsequent
mixers. The overall gain of the RF receiver is 14 dB, plus or minus 1.4 dB.
The ASR-9 amplifier has an AGC attenuator at the output of its first stagewhich is controlled
by the digital processor via a D/A converter to maintain constant gain and hold the receiver
output noise at a constant level. In addition to this feature, the ASR-9 receiver has a limiter
circuit inserted between the third and fourth IF amplifiers to limit the peak amplitude of the
receive signal to prevent A/D saturation. The limiter is adjustable to within + 2 dB with respect
to the signal level that saturatesthe A/D converter. There are three stagesinvolved in the AGC
amplifier. The fourth stage is used to boost the signal to the level required by the A/D converter.
The output of the fourth stage is applied to a phasedetector input through the bandpassfilter and
finally by its amplifiers. The overall bandpass is set to 923 kilohertz at the -60 dB point
corresponding to the transmitter pulse phasecharacteristics.
Receiver calibration data is sent to the RF-IF receiver function from the synchronizer circuits.
The test functions include setting the AGC of the receiver and regulating the I&Q amplitude
phasebalance and DC offset. The test tone signal is also controlled by this function. The test tone
supplied from the active target channel via Jl-D is usedfor testing the circuit.
J. I&Q Development
A very comprehensively designed I&Q detector is used in the ASR-9 weather channel. The
description of the ASR-9 I&Q circuitry is found on page 2-137 of TI 63 10.28.
A coarse and fine digital conversion schemeis used to produce the 12-bit I&Q words used in
the weather channel. The ASR-9 weather channel provides A/D converter testing, a three-point
test to verify that the circuit is operating at specified levels, and a monotonicity test for the A/D
converter. Similar test functions may be applied to circuits in the WSP.
Analog data are derived from a logarithmic conversion of the sixth IF amplifier output video.
Timing for the D/A converter is provided by the receiver control (reference TI 6310.28, page
2-137). The I&Q video signals are connected through the analog switch to sample and hold
networks. Signals are appropriately amplified and sent on to the maintenancedisplay.
t
47
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